The subject invention relates to a lathe for the machining of hollow articles. In a patent to Renoux, U.S. Pat. No. 3,937,110, issued Feb. 10, 1976 and entitled "Lathe for Machining Hollow Parts", the assignee of said patent being the same as the assignee of the present invention, there is described a lathe for the inner machining of hollow workpieces of revolution comprising two carriages disposed symmetrically in relation to the rotational axis of the workpiece to be machined and capable of moving longitudinally and transversely in translation, parallel to a common plane passing through said axis, each of these carriages supporting at least one tool-holder bar which is designed so as to bear on the corresponding tool-holder bar of the other carriage, through the medium of at least one surface parallel to said common plane.
It is known that with such an arrangement, the tool-holder bars, bearing on each other, have no longer to support individually the cutting stress developed by their respective tool, as is the case with a conventional machine. They must simply withstand the torque resulting from the composition of two equal parallel forces opposite in direction, which completely changes the nature and the value of the stresses generated. Moreover, the reaction of the tools on the machined workpiece and the members of the machine which support it is also completely changed. Instead of a radial force tending to cause the spindle of the machine to bend, there only remains a torsional torque. These two effects together permit the section of chip removed at each pass to be considerably increased and, consequently, the speed of production to be increased in proportion.
In the above-mentioned patent, which is incorporated herein by reference, there are also described several variations of the invention and, particularly, different possible forms for the tool-holder bars.
The present invention has as its object an improvement of the tool-holder bars allowing the advantages of the above described invention to be obtained in a much simpler and also less costly way.
For this purpose, each tool-holder bar of a carriage is provided with a longitudinal channel whose opposite faces are parallel to said common plane and inside which of there slidingly fits a heel provided on the corresponding tool-holder bar of the other carriage.
Each bar may thus follow the transverse movement of the carriage with which it is integral, while bearing on the other bar through sliding bearing surfaces, this of course being within the limit of the transverse travel allowed by the relative dimensions of the channel and the heel.
Preferably, the opposite parallel faces of the channel are provided with longitudinal grooves for lubricating at a suitable pressure the sliding support between the bars. This lubrication may be effected for example by means of a tapping made in the tool spraying circuit.
Generally, each of the transverse carriages of the lathe will be equipped with a rotary turret supporting several tool-holder bars, e.g. three or four. In fact, numerous workpieces require more complex machining than simple boring and conical thread-cutting, which then requires tools of different shapes working successively.
In this case, and according to the present invention, the two turrets have a common rotational axis, one of these turrets being motive whereas the other, provided simply as a driven element, is rotated by means of the inter-bar connection.